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“Emu W» mm
2,49%,934:
A. R. DOUCE'H'TE
DIRECT READING CAPACITY METER
Filed July 4:, 1944
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HIS
A'I'TORNEY
Patented Jan. 17, 1950
2,494,934
UNITED STATES PATENT OFFICE
2,494,934
DIRECT READING CAPACITY METER
Adrian R. Doucette, Millvale, Pa., assignor to The
Union Switch & Signal Company, Swissvale,
Pa., a corporation of Pennsylvania
Application July 4, 1944, Serial No. 543,499
2 Claims. (01. 175-183)
1
My invention relates to direct reading capacity
meters.
view showing one form of apparatus embodying
A common method of measuring capacities uses
a. bridge circuit and the unknown capacity is
measured by a comparison with a standard. This
Referring to the drawing, the dot and dash
substitution method presents special problems
with small capacities because of the stray capaci
my invention.
-
rectangle CM designates a panel or case for
mounting the apparatus comprising the meter.
This case is provided with terminals for con
necting outside devices hereto, four terminals Ill,
ties of the bridge circuit elements. Also the ac
ll, I2 and I3 being shown. The terminals Ill and
curacy depends upon the calibration of the stand
H are used for connecting the capacitor to be
ard and the observer’s ability to determine the 10 measured to the meter and the terminals l2 and
increment corresponding to the unknown ca
is are used for connecting a suitable source of
pacity.
.
power to the meter, such as a battery, the positive
Accordingly, a feature of my invention is the
and negative terminals of the battery being con
provision of a novel and improved direct reading
nected to terminals l2 and I3, respectively, as
15 indicated by a plus and a minus sign. Five
capacity meter.
Another feature of my invention is the provision
switches SWI, SW2, SW3, SW4, and SW5 are
provided for manual adjustment of the meter.
of an improved direct reading capacity meter for
measuring small capacities.
The switches SW2, SW3, and SW4 are preferably
of the gang type and are operatively connected
Still another feature of my invention is the pro
vision of a novel capacity meter wherewith the 20 together as indicated by a dotted line I 4 for move
ment of these switches in unison. Each of these
tolerance of manufactured capacitors can be
checked.
Other features, objects and advantages [in
volving my invention will appear as the speci?ca
tion progresses.
I obtain the features, objects and advantages
embodying my invention by providing an oscil
lator, an amplitude limiter, a discriminator and
a voltmeter. The unknown capacity is connected
to the oscillator and the frequency of the oscilla
tions is, changed according to the value of the
unknown capacity. The oscillator is coupled to
three switches has ?ve di?erent positions identi
?ed by the numerals 0, 1, 2, 3, and 4. Switch SW5
is also provided with ?ve positions indicated by
25 the numerals 0, 1, 2, 3, and 4, but switch SWl
is a two-position switch having an open and a
closed position. It is to be understood that these
switches may have more or less positions than
those disclosed.
The oscillator of the meter comprises an elec
tron tube VI and associated circuits. Tube Vl
may be of any standard type, and as disclosed it
is an indirectly heated triode, the ?lament of
the amplitude limiter and any amplitude changes
which is heated in the usual manner. An anode
in the output of the oscillator due to varied in
ductance-capacitance ratio are smoothed out. 35 l5 of tube Vi is connected to positive power
terminal l2 through a resistor I6 and wire l1, and
The amplitude limiter is coupled to the dis
cathode 2d of the tube is connected to negative
criminator which converts frequency changes into
power terminal l3 through wire 25, intermediate
voltage changes, and the voltmeter is connected
terminal and a portion of an inductance winding
to the discriminator to read‘ the voltage changes. 40 2|, and wire 22 to form an anode circuit for the
The voltmeter scale is calibrated in units of ca
tube. Control grid l8 of tube VI is connected
pacitance so that it reads directly the value of
the unknown capacity. To read tolerance, a
through a grid leak bias unit consisting of re
sistor l9 and condenser 20 in multiple, to wire
standard capacitor of normal value for the
26 which is connected to terminal l0, and which
capacitors to be checked is connected to the meter 45 wire serves as one bus wire for'an ‘oscillating
and the meter balanced and the standard capaci
circuit including inductance winding 2| and a
tor removed. The various capacitors are sub
stituted for the standard, one at a time, and the
plurality of capacitors to be referred to shortly.
Wire 22, which is connected to the negative power
terminal I3 is also connected to terminal II and
voltmeter reads the tolerance, that is, it reads
the diiference between the particular capacitor 50 to a ground terminal 23, and this wire serves as
and the standard.
'
another bus wire for the oscillating circuit and
I shall describe one form of apparatus embody
ing my invention, and shall then point out the
as a ground connection for other circuits of the
meter to be described hereinafter. Two capaci
novel features thereof in claims.
'
tors Q and M, at least one Of which is preferably
‘ The accompanying drawing is a diagrammatic 55 adjustable, are included in the oscillating or tank
2,494,934
circuit by being permanently connected across bus
wires 22 and 2B in multiple with inductance wind
ing 2!. Four other capacitors A, B, C, and D
are connected to bus wires 22 and 26 through
switches SWI and SW2 to be included in the
oscillating circuit, the arrangement being such
that when switch SWI is closed capacitor A, B, C,
4
ing to position 4, 3, 2, or 1 of switch SW3. The
parts of the amplitude limiter are proportioned
for the tube V2 to function as a class C ampli?er
and thus with the anode circuit tuned to reso
nance at the frequency of the oscillations of the
oscillator an electrcmotive force having a fre
quency corresponding to the frequency of the
or D is included in the oscillating circuit accord
oscillations of the oscillator is induced in second
ing as switch SW2 is set at its 4, 3, 2, or 1 position.
ary winding 31 of coupling transformer TI and
Each of these capacitors A, B, C, and D is pref 10 the amplitude of such oscillations induced in
erably adjustable. Any unknown capacitor, such
secondary winding 31 is substantially constant
as a capacitor CX is included in the oscillating .
over a relatively wide variation in amplitude of
circuit by being connected to terminals 10 and II
of the meter. A by-pass condenser 53 is con
nected across the anode H‘: of tube VI and the
grounded bus wire 22.
It is clear that with switch SWI open and no
capacitor CX connected‘ across terminals I0 and
the oscillations supplied by the oscillator.
The discriminator includes a double diode tube
V3, the ?laments of which are heated in the usual
manner.
Anode 36 of one section of tube V3 is
connected to the top outside terminal as viewed
in the drawing of secondary winding 31 of cou
II, the frequency of the current supplied by the
pling transformer TI, and anode 38 of the other
oscillator is preselected by the position of the 20 section of tube V3 is connected to the lower out
capacitors Q and M, but that with switch SW1
closed and capacitors Q and M set at given posi
tions and no unknown capacitor connected to
terminals l0 and II, the frequency of the current
supplied by the oscillator can be preselected with
in limits according to the settingr of switch SW2.
That is, there are ?ve different ranges of fre
quencies available, namely, a ?rst range is es
tablished when switch SW2 is set at position 0
side terminal of secondary winding 31. Resistors
39 and 40 in series are connected across cathodes
4| and 42 of the two sections of tube V3 and the
junction terminal of resistors 39 and 40 is con
nected to midterminal of secondary winding 31 of
transformer '11 through a coil 43.
Also, a con
denser 60 is connected between primary winding
33 of transformer TI and the midterminal of
secondary winding 31, and condensers 50 and 5|
and capacitors Q and M only are included in the 30 are connected across resistors 39 and 40. respec
oscillating circuit, a second range is established
tively. The outside terminal of resistor 40 is con
when switch SW2 is set at position 1 and ad
nected to ground bus wire 22.
justable capacitor D is added to the oscillating
Tuning of the discriminator to the frequency
circuit, a third range is established when switch
ranges of the oscillator is effected through
SW2 is set at position 2 and adjustable capacitor
capacitors I, J, K, L, and -P. Capacitor P is
C is added to the oscillating circuit, a fourth
permanently connected across secondary winding
range when the switch SW2 is set at position 3
31, and capacitors I. .1, K, and L are connected
and adjustable capacitor B is included in the
across winding 31. through positions 4, 3. 2. and
oscillating circuit, and a ?fth range is provided
1, respectively, of switch SW4. Each of these
when the switch is set at position 4 and adjust
capacitors is preferably adjustable.
able capacitor A is included in the oscillating cir
Frequency changes appearing in the electro
cuit. Furthermore, with any given position of
motive force induced. in secondary winding 31 of
switch SW2 and an unknown capacitor CX con
transformer Tl are converted into voltage
nected to terminals 10 and H, the frequency of
changes across resistors 39 and 40 in the well
the oscillations supplied by the oscillator is 45 known manner.
a
changed according to the value of the unknown
A voltmeter VM of any suitable form is con
capacitor. The oscillations created by the oscil
nected across resistors 39 and 40 by having one
lator are applied to an amplitude limiter through
terminal connected to the ground bus wire 22 and
a connection including the condenser 21 as will
its
other terminal connected to top terminal of
50
appear shortly.
resistor 39 through switch SW5. At position 0 of
The amplitude limiter comprises an electron
switch SW5, the voltmeter is connected directly
tube V2 and associated circuits. As here shown,
to the resistor 39 and at the other positions 1, 2,
tube V2 is an indirectly heated pentode, the ?la
3, and 4 of the switch the resistors 44, 45, 46,
ment of the tube being heated in the usual con
and 41, respectively, are included in the connec
ventional manner. Tube V2 is provided with a
tion and serve as a multiplier of the voltmeter.
control grid circuit including control grid 28, re
Furthermore. voltmeter VM is preferably pro
sistor 29, ground wire 22 and cathode 30, and this
vided with different scales, each of which would
control grid circuit is connected to the oscillator
be calibrated to read corresponding units of ca
through the connection including condenser 21, as
explained hereinbefore. Power is supplied to 00 pacitance. By way of illustration it may be said
that the voltmeter VM has one scale calibrated
anode 34 of tube V2 through a voltage divider
to
read from 0 to 125 micromicrofarads, a second
consisting of resistors 3| and 32 connected across
scale to read from 0 to 350 micromicrofarads, a
the power terminals l2 and 13 through wires 11
third scale to read 0 to 1250 micromicrofarads,
and 22. The junction terminal of these two re
sistors is connected to anode 34 through primary 65 a fourth scale to read from 0 to 3500 micromicro
farads, and a ?fth scale to read between 0 and
winding 33 of a coupling transformer TI and
some still higher value of capacitance. Further
wire 35.
more, each of these scales would be multiplied as
To tune the anode circuits of tube V2 to
to the value of the capacitance through the dif
resonance at the frequency of the Oscillator, a
ferent positions of the switch SW5, each position
group of capacitors E, F, G, H, and N are provided,
each of which capacitors is preferably adjustable.
Capacitor N is connected permanently across pri
mary winding 33 of transformer TI and each of
the capacitors E, F, G, and H is connected across
of the switch and the respective resistor inter
posed in the connection thereby serving as a mul
tiplier of the reading of the voltmeter. In this
way the voltmeter VM is provided with a scale
winding 33 through another capacitor 48 accord 75 that corresponds to each frequency range of the
2,494,934
6
5
itor of a, nominal value for the capacitors to be
checked is connected to the terminals Ill and II.
tions of the switch SW2.
'
Capacitor N is adjusted for maximum indica
The capacity meter is prepared to measure
tion on the voltmeter, with capacitor P out of
capacitance of 'its lowest range by setting the
balance. Capacitor P is then adjusted for 0
switches SW2. SW3, SW4, and SW5 in their 0
reading of the voltmeter, which in this case
positions, switch SWI being closed. With no un
would preferably be one having a 0 center scale.
known capacitor CX connected to terminals l0
The standard capacitor is then removed and the
and H, the capacitor Q is set at its minimum
capacitors to be measured for tolerance are con
range, and capacitor M is set at about the center
of its," range. With this setting for the oscillator, 10 nected one at a time to the terminals l0 and
II. The variation of each capacitor from the
the oscillator supplies a given frequency of os
standard can be read directly on the scale of
cillation such as, for example. 300 kilocycles per
the voltmeter.
second. The capacitors N and P are adjusted
The meter CM can be used also to measure
for maximum readingr oi the voltmeter VM and
capacitance by the substitution method. Under
capacitor P is readjusted for 0 reading of the
such circumstances, the capacitors A, B, C, and
voltmeter. That is to say. the discriminator is
D would each be of a standard capacitance.
tuned to resonance at the frequency of the oscil
In the case the second range is to be used, the
lations supplied by the oscillator. and no voltage
capacitors H and L would be adjusted in the
is created across resistors 39 and I0. Capacitor
manner explained hereinbefore for 0 reading of
CX to be measured is next connected to the ter
the voltmeter. Capacitor D is then ‘removed by
minals l0 and II and this capacitor CS causes
opening the switch SWI and the unknown capac
a change. in the frequency of the oscillations
itor CX is connected to terminals l0 and II.
supplied by the oscillator in direct proportion
The difference between the capacitor GK and the
to the value of the capacitor CX. Any variation
in the amplitude of the oscillations is smoothed ‘. standard D is read on the voltmeter and in that
manner the total value of the capacitance of out at the amplitude limiter and oscillations of
capacitor CX is determined. In the other po
a corresponding frequency are induced in sec
sitions of the switches, the capacitors C, B, and
ondary winding 31 of transformer Ti and this
A would be ?rst used and then disconnected
change in the frequency of the oscillations is
from the circuit by the opening of the switch
converted to a corresponding voltage drop across
SWI and the capacitor to be measured connected
resistors 39 and 40. the voltage drop being directly
to terminals l0 and ii and its capacitance de
proportioned to the change in the frequency.
termined by the reading of the voltmeter plus
This voltage drop created across resistors 39 and
the value of the standard capacitor.
M is indicated on the scale of the voltmeter
A meter such as here disclosed has the ad
VM and. as explained hereinbefore. the scale is ~
vantages that capacitance can be read directly,
calibrated to read in units of capacitance. Thus
a relatively wide range of values measured for
the capacitance of the capacitor CX is read di
the various ranges of the meter, extremely small
rectly on the voltmeter. Assuming that the
capacitance can be measured and errors due to
scales of the voltmeter are calibrated in the man
oscillator as provided through .the different posi
ner explained hereinbefore. anv capacitor up to
stray
125 micromicrofarads can be measured by this
?rst range of the meter. To increase the range
avoided. [Also the meter has the further ad
vantages that one side of the test circuit is at
ground potential due to the use of a ground bus
and still use the same scale of the voltmeter.
the switch SW5 can be set at its different posi
tions 1. 2, 3. and 4 and the scale reading of the
voltmeter multiplied by a value predetermined
by the value of resistors 44. 45, 46. and 41.
To use the next range of the meter. the switches
SW2, SW3. and SWlarc set in position 1.. Ca
pacitor D is now set at substantially the center
of its range and capacitors H and L are adjusted
?rst for maximum reading of voltmeter VM and
capacitor L readjusted to cause the voltmeter
capacitance between circuit elements
wire 22 and therefore shielded lead wires can
be extended from terminals l0 and II to the
capacitor under test and the capacity of such
lead wires neutralized through the setting of
the capacitors Q and M.
It is to be understood that the meter is not
limited to the values and ranges of capacitance
used in the description and such values and
ranges are for illustration.
Although I have herein shown and described
but one form of direct reading capacity meters
connected to terminals l0 and II and the value 66 embodying my invention, it is understood that
various changes and modi?cations may be made
of the capacity is read on the second scale of
therein within the scope of the appended claims
voltmeter VM, which second scale. by way of
without departing from the spirit and scope of
illustration, has been assumed to be calibrated
to read zero. The unknown capacitor CX is now
to read from 0 to 350 mi-cromicrofarads. when
,my invention.
the switch SW5 is set at position 0. The read 60
Having thus described my, invention, what I
ing of this scale can be multiplied by different
claim is:
predetermined amounts by setting switch SW5
1. In a capacity meter in which the frequency
at one of its different positions.
of the oscillations supplied by an oscillator is
Similarly, the meter can be used to measure
changed from an initial frequency according to
capacitance of still higher values by setting
a capacitor to be measured; an electron tube
switches SW2, SW3. and SW4 at their other
having an anode, a cathode and a control grid;
positions 2. 3, and 4. In each case the meter
a transformer having a ?rst and a second wind
would be ?rst adjusted in the manner explained
ing, an anode circuit including said ?rst wind
ing and a voltage source connected across said
hereinbefore and then the capacitor to be mea
sured would be connected to the terminals Ill 70 anode and cathode, a grid circuit including a
resistor connected across said grid and cathode
and ii and the value of such capacitor would
and adapted to receive oscillations, said resistor
be read directly on the scale of the voltmeter VM.
and voltage source proportioned for limiting the
To measure tolerance, that is, an allowed
ampli?cations of said electron tube, a discrimi
amount of variation from a standard, the meter
is set at its lowest range, and a standard capac 7' nator including two diodes each having an anode
2,404,984
and a cathode, said discriminator provided with
an input circuit which connects said second
winding across said anodes of said diodes and
with an output circuit which includes a pair
"
'
8
switch, said first switching means connected
across said ?rst winding to tune it to resonance
at any selected frequency of a plurality of dif
ferent frequency ranges according to the D081
of resistors in series connected across the oath
tion of the switch and the setting of the respec
odes of said diodes, a ?rst switching means in
tive adjustable capacitor, ,a second switching
cluding a. multiple position switch and a plu
means including a multiple position switch and
rality of adjustable capacitors one for each po
adjustable capacitors one for each position of the
sition of the switch, said ?rst switching means
switch, said second switching means connected
connected across said ?rst winding to tune it
across said second winding to tune it to reso
to resonance at any selected frequencyof a , nance at any selected frequency of a plurality of
plurality of different frequency ranges, a second
di?erent frequency ranges according to the po
switching means including a multiple position
sition of the switch and the setting of the re
switch and a plurality of adjustable capacitors
spective adjustable capacitor, said ?rst and second
one for each position of the switch, said second 15 switching means effective by the setting of their
switching means connected across said second
switches and capacitors to cause said discrimi
winding to tune it to resonance at any selected
nator to develop zero voltage across said pair of
frequency of a plurality of different frequency
ranges, a meter, a third switching means includ
ing a multiple position switch and a plurality
resistors when oscillations of any selected fre
quency of said plurality of different frequency
ranges are applied to said grid, a voltmeter hav
ing a zero center scale, a third switching means
including a multiple position switch and resistors
ing the meter to indicate a plurality of different
one for each position of the switch and operable
ranges of voltages, and said meter connected
to connect any one of its resistors in series with
across said pair of resistors through said third 26 said voltmeter to adjust the voltmeter to a plu
switching means to indicate a variation in the
rality of different voltage ranges, and said volt
frequency of the oscillations applied to said grid
meter connected across said pair of resistors
of the electron tube from any selected frequency
through said third switching means,'wheroby the
of any one of the plurality of said frequency
variation of the frequency of the oscillations ap
ranges.
30 plied to said grid to either side of said selected
of resistors and operable to connect any one of
its resistors in series with said meter for adjust
2. In a capacity meter in which the frequency
frequency is indicated by the reading of the
of the oscillations supplied by an oscillator is
voltmeter.
made to vary with respect to an initial fre
ADRIAN R. DOUCEI'I'E.
quency according as a capacitor to be measured
varies from a given standard capacitor; an elec 35
REFERENCES CITED
tron tube having an anode, a cathode and a
The
following
references are of record in the
control grid; a transformer having a first and
?le of this vpatent:
a second winding, an anode circuit including
UNITED STATES PATENTS '
said first winding and a voltage source con
nected across said anode and cathode, a grid
Number
Name
Date
circuit including a resistor connected across said
1,571,278
Kuhn ____________ __ Feb. 2, 1926
grid and cathode and adapted to receive oscil
1,663,086
Long __________ __ Mar. 20, 1938
lations, said resistor and voltage source propor
1,917,237
Barbulesco et al. ____ July 11, 1933
tioned to limit the ampli?cation of said tube, a
2,065,652
Carlson ________ __ Dec. 29, 1938
discriminator including two diodes each having
an anode and a cathode, said discriminator pro
vided with an input circuit which connects said
second winding across the anodes of said diodes
and with an output circuit which includes a
pair of resistors in series connected across the
cathodes of said diodes, a first switching means
including a multiple position switch and ad
Justable capacitors one for each position of the
2,146,073
2,209,959
2,218,642
2,228,367
Jennens et al _______ .._ Feb. 7,
Chittick et al. ____ __ Aug. 8.
Hathaway ________ __ Oct. 22,
Sanders, Jr. ______ __ Jan. 14,
1939
1940
1940
1941
2,273,110
Kimball'et al. ___..__ Feb. 17, 1942
2,280,678
Waymouth ____'..__.. Apr. 21, 1942
2,307,316
2,337,328v
Wolff ____________ __ Jan. 5, 1943
Hathaway _______ __ Dec. 21, 1943
2,362,503
Scott .._ __________ .._ Nov. 14, 1944
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